The political left is pressing the White House and Congress to inflict a wave of Pentagon budget cuts not seen since the post-Cold War 1990s.

Liberals are citing the debt crisis and troop drawdowns from Iraq and Afghanistan to argue that now is the time for the Defense Department to shed people, missions and weapons after a decade of doubling arms spending after the Sept. 11 terrorist attacks.

The proposals, including one from the Center for America Progress, go well beyond President Obama’s call in April for $400 billion in defense cuts over 12 years. The center — run by John Podesta, who served as chief of staff to President Clinton — wants that much in reductions over the next three years and $1 trillion from what had been projected increases over the next decade.

Some House Democrats, led by Rep. Barney Frank of Massachusetts, also have called for $1 trillion in cuts.

“I think this is the time because of a combination of the deficit and the changing way in which we’re going to deal with threats from groups like al Qaeda,” said American Progress’ Lawrence Korb, a longtime defense analyst in Washington.

Mr. Korb said the Obama administration has dumped President George W. Bush’s overall war strategy of preemptive attacks against terrorist states, and he cited just-retired Defense Secretary Robert M. Gates’ warning against any future land wars in the Middle East.

The bottom line is that the center wants projected increases ended and the overall arms budget reduced to $500 billion by 2016, which would be $111 billion below the Pentagon’s already pared-down projection.

“Gates said we don’t have to go back to Cold War levels,” Mr. Korb said. “Well, we’re above Cold War levels. And that’s part of the problem.”

Gordon Adams, a defense budget official in the Clinton White House, told the House Budget Committee this month that Mr. Obama’s $400 billion number “is a very small step.” He endorsed more than doubling that figure.

The Pentagon has not heard such rhetoric since the Berlin Wall fell and Presidents Clinton and George H.W. Bush squeezed as much as 35 percent out of intelligence and defense spending.

After al Qaeda’s attack on the United States, defense proponents said such a deep downturn had been a mistake, leaving intelligence agencies and some aspects of the military not ready to fight a global war against terrorists. Now, they say, America is about to repeat the mistake, as China and Iran flex their muscles and radical Islam remains a global threat.

Daniel Goure, an analyst at the pro-business Lexington Institute, said the left has it all wrong. The Pentagon needs more money, unless it abandons or curtails its presence in Europe, the Middle East and Asia, he said.

“You’d better change our military approach to the world,” said Mr. Goure. “If you do what we did the last time — which is essentially salami slice, take bits and pieces from everything and everybody — then you are essentially going to back where you were after Vietnam and at the end of the Cold War drawdown. Too many missions. Too many deployments. Not enough stuff. Not enough people.”

The Center for American Progress also proposes a list of weapons terminations and troop cutbacks.

The number of V-22 tilt-rotor aircraft would be stopped at about 150. The next-generation workhorse jet fighter, the F-35 — which is mired in big cost overruns — would be bought only for the Air Force, not the Navy or Marine Corps.

The Navy’s 11 carriers — a key way America projects immediate air power overseas — would be trimmed to nine, and with it other surface ships. A full third of 150,000 troops in Europe and Asia would be ordered home.

“You may not be able to keep as many carriers forward-deployed,” said Mr. Korb. “You would have to surge them, but I don’t see any missions you could not do.”

However, reducing the number of active carriers to nine means only three typically would be deployed at one time, possibly leaving the Pacific without a surface ship strike force.

“If the Chinese are going to threaten Taiwan, they’re going to do it with short-legged stuff, short-range ballistic missiles, right from shore,” Mr. Korb said. “We can’t do it that way. If the threat were Mexico, not to worry. We build diesel submarines and short-range fighters, and we’d call it a day.”

Such drastic cuts would face strong Republican opposition.

A spokesman for Senate Minority Leader Mitch McConnell, Kentucky Republican, said the GOP would never approve cuts of $1 trillion.

House Budget Committee Chairman Paul Ryan, Wisconsin Republican, released a detailed budget plan that calls for modest defense drawdowns over five years. He argued that the Defense Department’s total budget share already has decreased from 25 percent to 20 percent.

A smattering of conservatives are advocating more shrinkage. Some Republicans on Mr. Obama’s deficit commission supported cuts above $400 million.

With all troops due to be pulled out of Iraq this year and Afghanistan by 2014, the Pentagon could save $100 billion annually on those two accounts alone. Mr. Gates instituted more than $100 billion in savings, although some of that money was redirected into other arms programs.

The next phase is likely to be revealed in Mr. Obama’s fiscal 2013 budget in February or in some grand deficit-reduction agreement between him and Congress.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said this year: “We can’t hold ourselves exempt from the belt-tightening. Neither can we allow ourselves to contribute to the very debt that puts our long-term security at risk.”

Defense Secretary Leon E. Panetta, who proved a hawkish director of the CIA, vowed to Congress that he would not let the military go hollow as it did in the late 1970s.

On July 8, he urged the White House and Congress to base cuts on a strategy. He expressed his concern about negotiators who would just “just pick a number and throw it at the Defense Department without really looking at policy, without looking at what makes sense.”